Methods for using sulfidized red mud

ABSTRACT

Toxic substances such as heavy metals are extracted from a medium using a sorbent composition. The sorbent composition is derived by sulfidation of red mud, which contains hydrated ferric oxides derived from the Bayer processing of bauxite ores. Exemplary sulfidizing compounds are H 2 S, Na 2 S, K 2 S, (NH 4 ) 2 S, and CaS x . The sulfur content typically is from about 0.2 to about 10% above the residual sulfur in the red mud. Sulfidized red mud is an improved sorbent compared to red mud for most of the heavy metals tested (Hg, Cr, Pb, Cu, Zn, Cd, Se, Th, and U). Unlike red mud, sulfidized red mud does not leach naturally contained metals. Sulfidized red mud also prevents leaching of metals when mixed with red mud. Mixtures of sulfidized red mud and red mud are more effective for sorbing other ions, such as As, Co, Mn, and Sr, than sulfidized red mud alone.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 12/781,965, filed May 18, 2010, which is a division of U.S. application Ser. No. 12/537,907, filed Aug. 7, 2009, now U.S. Pat. No. 7,807,058, which is a division of U.S. application Ser. No. 11/277,282, filed Mar. 23, 2006, now U.S. Pat. No. 7,763,566, the disclosures of which are hereby incorporated by reference. The disclosure of U.S. application Ser. No. 12/796,066, filed Jun. 8, 2010, and being a continuation-in-part of application Ser. No. 11/277,282, filed Mar. 23, 2006, now U.S. Pat. No. 7,763,566, is also incorporated hereinto by reference.

FIELD OF THE INVENTION

The present invention is generally directed to sorbents and methods for use of said sorbents in the treatment of fluids such as waste streams to remove undesired contaminants contained therein and particularly for the facile extraction of heavy metals inter alia from liquid and gaseous streams, as well as removal of the sorbed heavy metals by solids/fluid separation means.

DESCRIPTION OF RELATED ART

Heavy metal contaminated flue gases and liquids from various sources (ground, stream, runoff, mines, petroleum, industrial waste, sanitary waste) are among the most dangerous and difficult environmental problems facing the world today. An especially serious problem is posed by toxic metals in such streams. Among these metals are mercury, chromium, cobalt, nickel, copper; zinc, silver, gold, cadmium, lead, selenium, and transuranic elements.

Mercury contamination of the environment is the subject of increasing attention because it eventually accumulates at very high levels in the bodies of large predatory fish such as tuna, swordfish, and sharks. A major concern is the atmospheric release of mercury from coal fired power plants, currently estimated at 46 tons per year in the United States. The Environmental Protection Agency (EPA) has identified women of childbearing age as especially threatened because of possible neurological damage to unborn children. It has been estimated that 8% of women in this category have a methyl mercury blood level above 5.8 ppb.

On Dec. 14, 2000, the EPA issued a determination that their agency must propose new regulations under the Clean Air Act to control mercury emissions from coal and oil fined power plants by Dec. 15, 2003. One proposal was to reduce mercury emissions from power plants by 90% by 2007. According to an article in Forbes (Apr. 14, 2003, page 104) such regulation “could cost the power industry at least 8.8 billion dollars per year.” Other, more recent proposals such as the Clear Skies Act call for a 70% reduction in mercury emissions over 15 years.

At present, a major control technology for mercury is the use of activated carbon treatment of flue gases from power plants. Activated carbon currently sells for about 45 cents per pound ($900 per ton) but the disposal or possible regeneration of mercury-sorbed activated carbon present unresolved problems at this time.

Red mud is an undesirable by-product and major pollutant from the Bayer Process. Bayer caustic leaching of bauxite is the principal process for production of alumina. This process relies on the solubility of aluminous minerals in hot (e.g., 125-250° C.) sodium hydroxide solution and the insolubility of most of the remaining minerals (iron, titanium compounds and silica), which are either insoluble or react and re-precipitate. The insoluble, iron rich residue byproduct is known as “red mud.” Red mud can contain from about 17.4 to 37.5% iron (Fe) (Bauxite Residue Fractionation with Magnetic Separators, D. William Tedder, chapter 33, Bauxite symposium, 1984, AIME 1984). Red mud is a complex mixture of finely divided hydrated iron oxides with a wide variety of lesser minerals (Al, Na, Ti, Si, Ca, Mg) and traces of over a score of other elements (Cr, Ni, Zn, Pb, As, etc). These hydrous iron oxides have extraordinary sorptive and complexing properties.

Red mud is a very hydrophilic, high pH slime which is extremely difficult to dewater by filtration or sedimentation means. This complicates and limits its utility as a sorbent in aqueous systems.

Red mud has been proposed as a sorbent for heavy metals, cyanides, phosphates, and the like (David McConchie, Virotec website: virotec.com/global.htm). However, the sorptive and release properties of red mud are not always complementary. Depending on the source of a particular red mud, it can also leach out significant amounts of toxic pollutants such as radioactive thorium, uranium, chromium, barium, arsenic, copper, zinc, cobalt and selenium, as well as lead, cadmium, beryllium, and fluorides.

The potential problems involved with use of red mud to control pollution are highlighted in an e-newsletter article entitled “The Great Red Mud Experiment that Went Radioactive”—Gerard Ryle, May 7, 2002 (smh.com.au/articles/2002/05/06/1019441476548.html). This experiment conducted by the Western Australian Agricultural Department involved placing 20 tonnes of Alcoa red mud per hectare on farmland in order to stop unwanted phosphorous from entering waterways. An unintended result of this application was that runoff waters showed excessive quantities of copper, lead, mercury, arsenic, and selenium. Emaciated cattle grazing on such land exhibited high chromium, cadmium, and fluoride levels. Each hectare contained up to 30 kilograms of radioactive thorium. The disastrous red mud application test was abruptly terminated after five years.

It is therefore evident that extreme caution must be exercised in selecting and testing red mud before attempting to use it to sorb toxic compounds.

Furthermore, the capacity of red mud to capture and hold toxic substances such as mercury and related metals is not adequate to eliminate traces of these metals in leachate. The possibility also exists that sorption of one toxic pollutant may release other pollutants. As a result, use of red mud as a sorbent to achieve drinking water standards can be problematic.

Prior attempts to produce useful materials from red mud are exemplified by Yu et al in U.S. Pat. No. 4,560,465. In this patent, Yu et al disclose the presulfiding of red mud using hydrogen and H₂S inter alia at temperatures ranging from about 200° F. to 3000° F. and pressures ranging from 50 to 3500 psig, these conditions being sufficiently severe to convert substantially all of the iron, namely, both Fe₂O₃ and the Fe, Al, Ca oxide hydrates, to pyrrhotite, Fe_(1−x)S, and particularly Fe₇S₈. The pyrrhotitic material thus formed is dehydrated and is less reactive as a sorbent than is red mud per se. The pyrrhotitic materials of Yu et al are used as a catalytic agent for cracking hydrocarbons, these materials apparently providing a more efficient hydrogen distribution for the catalyst of Yu et al as noted in column 4, lines 36-40 of the aforesaid patent. The red mud products treated according to the teaching of Yu et al are ineffective for use as sorbents.

Sulfidized red mud prepared according to the invention, that is, under relatively mild conditions compared to the severe temperatures and pressures of Yu et al as well as without the use of hydrogen, is an amorphous material useful as a sorbent which typically does not contain pyrrhotites as does the catalyst of Yu et al which is not useful as a sorbent.

There remains a need for improved sorbents for extracting toxic compounds such as mercury and other heavy metals from waste streams and the like and for extracting undesirable contaminants from other fluids.

SUMMARY OF THE INVENTION

The present invention, according to one aspect, is directed to a sorbent comprising the reaction product of a sulfidizing compound and red mud. Red mud contains hydrated ferric oxides derived from Bayer processing of bauxitic ores. The sorbent is particularly useful for sorbing toxic substances from a medium, such as heavy metals present in a liquid or gaseous stream. Exemplary sulfidizing compounds include H₂S, Na₂S, K₂S, (NH₄)₂S, and CaS_(x). The sulfur content of the reaction product typically is from about 0.2 to about 10% above the residual sulfur in the red mud.

According to one aspect of the invention, potable water (e.g., meeting drinking water standards) is prepared by treating contaminated water with a sulfidized red mud sorbent.

According to another aspect of the invention, heavy metals, whether in elemental or ionic form, such as mercury are sorbed from flue gases of coal- or oil-fired power plants by treating the flue gases with a sulfidized red mud sorbent. Other applications include but are not limited to treatment of waste effluents from municipal waste combustors, hazardous waste combustors, hospital waste combustors, cement kilns, and industrial boilers inter alia.

According to another aspect of the invention, heavy metals are sorbed from mine drainage waters by treating the mine drainage waters with a sulfidized red mud sorbent.

According to yet another aspect of the invention, heavy metals are sorbed from a hydrocarbon stream, such as a petroleum stream, by treating the stream with a sulfidized red mud sorbent.

The sorbent of the present invention is more effective for sorbing various contaminants, such as mercury, which are less effectively sorbed by red mud. Conversely, red mud is effective for sorbing other contaminants, such as arsenic, which are not effectively sorbed by the sulfidized red mud sorbent. Thus, some treatments can benefit by using both red mud and sulfidized red mud, either in the same sorbent composition or in separate treatment stages. Such sorbent combinations potentially can allow for the extraction of a wider range of contaminants.

Sulfidized red mud as disclosed herein is an effective sorbent for removing a wide variety of noxious materials from fluids ranging from contaminated water to flue gases and further permits more facile recycling of caustic liquors in aluminum production by sulfidizing red mud resulting from such processes.

DETAILED DESCRIPTION OF THE INVENTION

The present invention has applicability in removing contaminants from a wide variety of mediums, non-limiting examples of which include flue gases and liquids from various sources such as groundwater, water streams, sanitary waste waters, runoff, mines, petroleum streams, and industrial waste streams. Of particular interest is sorbing heavy metals, such as mercury (Hg), chromium (Cr), lead (Pb), copper (Cu), zinc (Zn), silver (Ag), gold (Au), cadmium (Cd), selenium (Se), thorium (Th), and uranium (U), from such mediums. The metal(s) may be present as ions, as free elements, or in compounds with other elements.

The sorbents of the present invention can be used for the preparation of potable water, e.g., meeting drinking water standards. Other exemplary applications include sorbing heavy metals, such as mercury, from flue gases of coal- or oilfired power plants, mine drainage waters, or hydrocarbon streams such as petroleum streams. The sorbents of the invention also remove H₂S and sulfide gases from effluent streams as well as volatile organic compounds such as dioxins and furans.

The sorbent can be prepared by the sulfidation of red mud, which contains hydrated ferric oxides derived from the Bayer processing of bauxitic ores. Sulfidation can be achieved by reacting the red mud with one or more sulfidizing compounds such as H₂S, Na₂S, K₂S, (NH₄)₂S, and CaS_(x). Unlike red mud, which is very hydrophilic, the sulfidized red mud is lyophobic and more readily dewatered. As a result, sulfidized red mud exhibits significantly faster filtration and settling rates than those exhibited by red mud.

The relative amount of the sulfidizing compound preferably is selected so that the sulfur content of the reaction product is from about 0.2 to about 10% above the residual sulfur content of the red mud. The weight ratio of sulfidizing compound to red mud will vary on the type of sulfidizing compound used and the desired level of sulfidation for a particular end use. Most often, the sulfidizing compound and red mud are combined at a weight ratio of from about 1:40 to about 1:4, more usually from about 1:25 to about 1:6, and even more usually from about 1:20 to about 1:8.

The conditions under which the red mud can be sulfidized depend on such factors as the identity of the sulfidizing compound(s) and the intended use of the resulting sorbent. In some cases, sulfidation can be accomplished by mixing red mud and the sulfidizing compound at ambient temperature and atmospheric pressure. In general, higher sulfur contents can be obtained when the reaction is carried out at elevated temperatures and/or elevated pressures. Sulfur content in the reaction product also can be influenced by factors such as the sulfur content of the sulfidizing agent. For example, compounds with higher sulfur contents, such as calcium polysulfide, typically yield products having higher sulfur contents.

When using gaseous sulfidizing compounds, such as hydrogen sulfide (H₂S), it is often preferable to conduct the reaction at elevated temperature and/or elevated pressure to increase the rate of reaction and the sulfur content of the resulting sorbent. Suitable exemplary reaction temperatures range from about 40 to about 200° C., often from about 80 to about 120° C. The reaction pressure typically ranges from about 1 to about 225 psi, often from about 30 to about 70 psi (absolute).

A particular use of the present technology resides in the treatment of red mud, a by-product of the Bayer process in the production of aluminum, the red mud being sulfidized according to the invention either as a stream of red mud exiting the bauxite treatment step or after an initial storing of a red mud/caustic slurry. Such treatment permits more facile recycling of at least portions of caustic liquor occurring as a portion of the red mud by-product due to the resulting sulfidized red mud having a less hydrophilic nature than does red mud per se. Accordingly, sulfidized red mud can be removed from the caustic liquor more easily by static sedimentation in settling ponds or by accelerated sedimentation such as by use of hydroclassifiers including centrifugal or cyclonic action than can red mud. Sulfidized red mud can also be more easily removed from the caustic liquor by filtration than can red mud.

Treatment of waste water to reduce or remove phosphates, TDS (Total Dissolved Solids) including organic material and bacteria can also be effected by the use of sulfidized red mud. In such treatment, it is preferred to admix a slurry of sulfidized red mud with the waste water followed by separation of the sulfidized red mud by separation processes including filtration, centrifugation, or sedimentation including static sedimentation such as settling or accelerated sedimentation such as by hydroclassification. Use of sulfidized red mud in slurry form directly after sulfidization without filtering and drying is preferred for most use applications.

Drying of sulfidized red mud prior to use for waste water treatment inter alia causes the sulfidized red mud to be less hydrophilic so that settling of the sulfidized red mud occurs more rapidly via static sedimentation. Similarly, accelerated dewatering processes and filtration processes also occur more rapidly when the sulfidized red mud is dried although sorbing activity is decreased. Concentration of sulfidized red mud by sedimentation or filtration prior to drying can be efficacious and reduces the cost of drying.

Sulfidized red mud can also be spray-dried to particularly improve filtration rates when such dried sulfidized red mud is used to form a filtration medium. In such applications, spray drying of sulfidized red mud improves filtration rate two or three-fold compared to spray drying of red mud per se. Thermal exposure of the sulfidized red mud in a spray drier at an outlet temperature of 100° C. for 15 to 30 seconds is preferred. Spray-dried sulfidized red mud can advantageously be used to sorb contaminated water of toxic material including toxic metals followed by separation of the sulfidized red mud from the resulting purified water.

A slurry of sulfidized red mud such as can be produced by sulfidization of red mud after discharge from a Bayer process exhibits enhanced utility relative to dried sulfidized red mud due to cost savings occurring through avoidance of filtration and drying stages, retention of high alkalinity as can be lost in a filtration step, ease of shipping, processing and mixing with a fluid which is to be treated with sulfidized red mud. In important uses of sulfidized red mud as a sorbent, a slurry of sulfidized red mud can be used directly by bringing the slurry into contact with a flue gas, acid mine waste streams or other fluid advantageously sorbed by sulfidized red mud. Further, shipping of a slurry of sulfidized red mud is comparable in cost to shipping dried sulfidized red mud.

Use of sulfidized red mud includes production of potable water through treating waste water; altering the hydrophilic nature of red mud to enhance dewatering of red mud; and, reduction of the size of red mud impounds by enhanced removal of liquid from red mud once the red mud is sulfidized.

In one embodiment of the present invention, the sorbent is slurried together with the medium containing the contaminant(s) to be extracted. Suitable mixing equipment can be used to provide sufficient contact between the sorbent and the contaminant(s). The sorbent, which forms a complex with the contaminant(s), can then be separated from the slurry using one or more conventional techniques such as filtration, sedimentation, or centrifugation.

In an alternative embodiment of the present invention, the sulfidized red mud sorbent is processed into pellets or the like using conventional pelletizing or extrusion equipment. Preparing the sorbent in pellet form can simplify its handling and/or use. The pellets may be incorporated into filters of conventional construction for use in a variety of industrial or consumer filtration applications, such as filters usable for preparing potable water.

It has been found that the sulfidized red mud sorbent is effective for sorbing various contaminants, such as mercury, which are not effectively sorbed by red mud. On the other hand, red mud is effective for sorbing other contaminants, such as arsenic, which are not effectively sorbed by sulfidized red mud. For the treatment of mediums having contaminants in both of these categories, the use of red mud and sulfidized red mud in tandem, either in the same sorbent composition or in sequential treatment stages (e.g., red mud followed by sulfidized red mud) can be more effective than using either sorbent alone.

EXAMPLES Example 1

This example shows the preparation of red mud. A 1 kg sample of red mud received from Sherwin Alumina Company of Corpus Christi, Texas was slurried at 15% solids in demineralized water and filtered on a Buchner funnel. The resulting filter cake was re-slurried with demineralized water, re-filtered, and used as the starting material in Example 2. The red mud thus prepared is used as detailed herein in remaining examples.

Example 2

This example illustrates the preparation of sulfidized red mud using hydrogen sulfide (H₂S). Washed red mud (100 g) from Example 1 was slurried in demineralized water at 15% solids and the stirred slurry was saturated with hydrogen sulfide for 30 minutes at ambient temperature. The sample was dried overnight at 100° C. and the resulting cake was pulverized.

Example 3

This example shows the preparation of sulfidized red mud using H₂S under pressure in a Parr Bomb. The sulfidation procedure of Example 2 was repeated using a Laboratory Parr Bomb. After saturation of the slurry with hydrogen sulfide gas, the bomb was sealed and heated four hours at 100° C. while stirred. The bomb was then cooled, depressurized and the contents filtered, dried, and pulverized.

Example 4

This example illustrates the preparation of sulfidized red mud using ammonium sulfide (NH₄)₂S. Red mud (200 g) was dispersed in 600 grams of deionized (DI) water in a Waring Blender for 5 minutes. Ammonium sulfide (10 g) was added and the slurry was heated with stirring on a hot plate for 1 hr. at 60° C. It was then filtered and dried at 90° C.

Example 5

This example shows the preparation of sulfidized red mud using sodium sulfide (Na₂S). The procedure of Example 2 was repeated using sodium sulfide instead of ammonium sulfide.

Example 6

This example illustrates the preparation of sulfidized red mud using calcium polysulfide (CaS_(x)). The procedure of Example 2 was repeated using 33.5 g of 30% solution of Cascade calcium polysulfide.

Example 7

The following table summaries the sulfur content of the red mud (RM) of

Code Description Example S (wt %) RM Red Mud 1 0.19 SRM-2 Sulfidized Red Mud H2S 2 0.48 SRM-3 Sulfidized Red Mud H2S w/ Pressure 3 0.90 SRM-4 Sulfidized Red Mud (NH4)2S 4 0.46 SRM-5 Sulfidized Red Mud Na2S 5 0.62 SRM-6 Sulfidized Red Mud CaSx 6 1.19

A complete analysis of RM, SRM-3, SRM-4, SRM-5, SRM-6 is given in Table A below. The analysis reveals that filtration and washing during preparation of sulfidized red mud extracts sodium chloride (except for SRM-5) and reduces bound water in the red mud. It is notable that very small amounts of reacted sulfur have such a profound effect on the chemical and physical properties of red mud.

TABLE A Weight % Code Description Na₂O MgO Al₂O₃ SiO₂ P₂O₅ S Cl K₂O CoO TiO₂ MnO Fe₂O₃ BaO RM Control 4.73 0.12 17.1 8.23 1.14 0.19 0.20 0.06 6.79 6.12 0.73 39.9 0.02 SRM-3 H₂S (b) 3.94 0.14 14.6 9.14 1.38 0.90 0.11 0.05 6.36 6.79 0.90 46.2 0.02 SRM-4 (NH₄)₂S 4.39 0.13 17.9 9.24 1.26 0.46 0.15 0.04 8.82 6.95 0.85 42.3 0.02 SRM-5 Na₂S 5.20 0.11 17.2 8.56 1.15 0.62 0.15 0.03 7.53 6.22 0.75 41.5 0.02 SRM-6 CaS_(x) 4.44 0.09 16.2 8.41 1.29 1.19 0.14 0.04 9.32 6.60 0.81 41.2 0.02 PPM Code Description V Cr Co Ni W Cu Zn As Sn Pb Mo Sr U RM Control 1100 1258 99 680 16 119 416 47 247 144 <10 424 65 SRM-3 H₂S (b) 1252 1506 121 860 23 138 458 44 177 180 <10 498 57 SRM-4 (NH₄)₂S 1093 1379 120 762 30 146 648 46 155 176 13 447 36 SRM-5 Na₂S 942 1272 103 695 24 130 504 31 181 159 11 387 39 SRM-6 CaS_(x) 1054 1364 113 780 29 138 471 49 155 165 13 431 50 PPM Code Description Th Nb Zr Rb Y RM Control 186 188 1757 24 673 SRM-3 H₂S (b) 199 207 1503 21 831 SRM-4 (NH₄)₂S 159 153 1888 <10 748 SRM-5 Na₂S 123 148 1659 <10 695 SRM-6 CaS_(x) 146 146 1767 <10 745

Example 8

This example illustrates leaching of red mud and sulfidized red mud. In part (a), a slurry of red mud (50 g) and demineralized water (450 ml) was prepared, mixed for 30 minutes, and filtered. The filtrate was acidified with 2 ml concentrated nitric acid and analyzed by ICP using EPA3050 and EPA6010 methods.

In part (b), the procedure of part (a) was repeated using sulfidized red mud from Example 2.

Results are given in Table I and show that leachate from sulfidized red mud (SRM) gave a lower content of heavy metals (low parts per billion) than leachate from the red mud (RM) in every case except Cd, where the difference was insignificant.

TABLE I Metal Concentration in Leachate (ppm) Hg As Cd Cr Pb Se SRM 0.0026 ND* 0.0013 0.0044 ND ND RM 0.0032 0.096 ND 0.0510 0.0064 0.017 *ND—Not detectable, below limits

Example 9

This example shows mercuric ion (3.5 ppm) sorption by sulfidized red mud. Ten grams of sulfidized red mud from Example 3 was slurried 30 minutes with 1 kg demineralized water containing 3.5 ppm mercury (5.66 ppm mercuric nitrate). The slurry was filtered and analyzed for mercury (Hg⁺⁺) by ICP (Method EOA 245.1).

Example 10

This example illustrates mercuric ion (3.5 ppm) sorption by red mud. Example 9 was repeated using red mud.

Example 11

This example shows mercuric ion (22 ppm) sorption by sulfidized red mud. Example 9 was repeated using 22 ppm mercury (Hg).

Example 12

This example illustrates mercuric ion (22 ppm) sorption by red mud. Example 11 was repeated using red mud.

Example 13

This example shows mercuric ion (41 ppm) sorption by sulfidized red mud. Example 9 was repeated using 41 ppm mercury (Hg⁺⁺).

Example 14

This example illustrates mercuric ion (41 ppm) sorption by red mud. Example 13 was repeated using red mud.

Results of Examples 9-14 are summarized in Table II and demonstrate the superior performance of sulfidized red mud compared to red mud for sorption of mercuric ion from aqueous solutions.

TABLE II Mercuric Concentration Example In Filtrate Sorbent Control  3.5 ppm none  9 0.56 ppm red mud 10  0.2 ppm sulfidized red mud Control 22.0 ppm none 11  8.0 ppm red mud 12 0.22 ppm sulfidized red mud Control 41.0 ppm none 13 23.4 ppm red mud 14 0.04 ppm sulfidized red mud

Example 15

This example shows mercury (metal) sorption from vapor phase by sulfidized red mud and by red mud (spray absorbed). In part (a), one gram of mercury metal was placed in a two necked round bottom (RB) flask on a supported heating mantle. One neck of the flask was open and the second neck was connected with a Teflon® tube to an aperture in the inlet duct of a spray dryer. The mercury was heated to 300° C. while hot air was aspirated through the vessel. Mercury vapor was entrained in the air as it was drawn into the inlet air duct of the spray dryer heated to 300° C. A slurry of 50 g SRM (Example 3) in 450 ml demineralized water was sprayed by a rotary atomizer operating at 30,000 rpm. The feed rate of SRM was regulated to produce an outlet temperature of 100° C. from the dryer.

In part (b), the procedure of part (a) was repeated using RM (Example 1) instead of SRM.

The mercury content of the spray dried SRM from part (a) and the RM from part (b) are tabulated in Table III and demonstrate that the SRM had a significantly improved sorption of mercury.

TABLE III Hg Concentration (ppm) 15(a) SRM-3 61.0 15(b) RM-1 8.1

SRM-3 absorbed 7.5 times as much mercury as RM-1 when spray dried at 300° C. inlet and 100° C. outlet in the presence of an air stream contacted by mercury heated to 250° C. Sulfidized red mud is significantly superior to red mud as a sorbent for elemental mercury metal vapor.

Example 16

This example shows mercury (metal) sorption from vapor phase by sulfidized red mud and by red mud (spray absorbed). Example 15 was repeated except that a slurry of 100 g SRM in 900 ml demineralized water was used. On completion of drying, a 50 g sample (a) was set aside for analysis and 50 g was re-slurried in 450 ml demineralized water and re-dried (b). Samples 16a and 16b were analyzed for mercury.

This experiment was then repeated using 100 g RM to furnish samples 16c and 16d, which were analyzed. The results of parts (a)-(d) are shown in Table IV below.

TABLE IV Hg Concentration (ppm) 16(a) SRM-3 1st pass 95 16(b) SRM-3 2nd pass 340 16(c) RM-1 1st pass 43 16(d) RM-1 2nd pass 48

As evident from Table IV, SRM-3 was more than twice as efficient as RM-1 on the first pass and about seven times as efficient as RM-1 on the second pass. The results show that the affinity of SRM-3 for mercury improves with increased exposure to mercury, indicating an induction effect.

Example 17

This example illustrates mercury (metal) sorption from vapor phase by sulfidized red mud (a) and red mud (b) using a column. In part (a), one gram of mercury was placed in a two necked RB flask supported on a heating mantle. One neck of the flask was open (vented) and the second neck was connected to a vertical tube 20 cm long and 2.5 cm diameter half filled with spray dried sulfidized red mud. A slight vacuum was applied to the open end of the packed tube and regulated to fluidize the spray dried sulfidized red mud while the mercury in the flask was heated to 300° C. The aspiration was continued for 20 minutes, the tube was disconnected from the RB flask and the sulfidized red mud contents analyzed for mercury by ICP.

In part (b), the procedure of part (a) was repeated using spray dried red mud, after which the red mud was also submitted for mercury analysis by ICP.

Results of the above experiment are tabulated in Table V and demonstrate increased sorption of mercury vapor by sulfidized red mud (SRM-3) compared to red mud (RM-1).

TABLE V Hg Concentration (ppm) 17(a) SRM-3 72 17(b) RM-1 25

Example 18

This example shows sorption of mercury (metal) from naphtha by sulfidized red mud (a) and red mud (b). In part (a), a solution of 500 ml naphtha containing 100 ppb of mercury was slurried with 10 grams of spray dried sulfidized red mud (SRM) for 30 minutes. The resulting slurry was filtered, and the SRM filter cake was dried for 1 hour at room temperature and analyzed for mercury by ICP.

In part (b), the procedure of part (a) was repeated using red mud (RM).

Results of parts (a) and (b) are shown in Table VI and reveal the increased capture of mercury from naphtha by sulfidized red mud (SRM-3).

TABLE VI Mercury (ppb) 18(a) SRM-3 filtrate 46 18(b) RM-1 filtrate 21

Example 19

This example shows sorption of chromium (III) by sulfidized red mud (SRM) and red mud (RM). In part (a), ten grams of SRM was slurried 30 minutes with 1 kg demineralized water containing 2.240 ppm chromium III. The slurry was filtered and the filtrate analyzed for chromium by EPA 200.9 method.

In part (b), the procedure of part (a) was repeated using 2.240 ppm chromium III and red mud (RM). The results are shown in Table VII below.

TABLE VII Chromium III (ppm) Control 2.240 19(a) SRM-3 filtrate 0.005 19(b) RM-1 filtrate 0.018

Results shown in Table VII demonstrate improved sorption of Chromium III by SRM-3 compared to RM-1.

Example 20

This example illustrates sorption of cobalt (II) by sulfidized red mud (SRM) and by red mud (RM). The procedures of Examples 19(a) and (b) were repeated using 2.75 ppm of cobalt II. The results are shown in Table VIII below.

TABLE VIII Cobalt II (ppm) Control 2.75 20(a) SRM-3 filtrate 0.013 20(b) RM-1 filtrate 0.046

Results in Table VIII show that SRM-3 has greater affinity for cobalt II than RM1, with the filtrate from SRM-3 containing less than ⅓ of cobalt II than that contained in the filtrate from RM-1.

Example 21

This example shows sorption of nickel (II) by sulfidized Red Mud (SRM) and by red mud (RM). The procedures of Examples 15(a) and (b) were repeated using 1.13 ppm nickel (II). The results are shown in Table IX below.

TABLE IX Nickel II (ppm) Control 1.13 21(a) SRM-3 filtrate 0.056 21(b) RM-1 filtrate 0.009

The results show nickel removal by SRM-3 was less efficient than by RM-1.

Example 22

This example illustrates sorption of copper (II) by sulfidized red mud (SRM-3) and by red mud (RM-1). The procedures of Examples 19(a) and (b) were repeated using 1.550 ppm, 6.250 ppm, and 30.500 ppm copper (II). The results are shown in Table X below.

TABLE X Copper II (ppm) Control A 1.550 22(a) SRM-3 filtrate <0.004 22(b) RM-1 filtrate 0.028 Control B 6.250 22(c) SRM-3 filtrate 0.038 22(d) RM-1 filtrate 0.054 Control C 30.500 22(e) SRM-3 filtrate 0.040 22(f) RM-1 filtrate 0.073

The results show a clear advantage of SRM-3 over RM-1 for copper removal over a 15-fold range of copper concentrations.

Example 23

This example shows sorption of zinc (II) by sulfidized red mud (SRM) and by red mud (RM). The procedures for Examples 15(a) and (b) were repeated using 1.850 ppm zinc (II) and 2.380 ppm zinc (II). The results are shown in Table XI below.

TABLE XI Zinc II (ppm) Control A 1.850 23(a) SRM-3 filtrate 0.009 23(b) RM-1 filtrate 0.035 Control B 2.380 23(c) SRM-3 filtrate 0.022 23(d) RM-1 filtrate 0.103

The results show SRM-3 is superior to RM-1 for zinc removal and yields filtrates with about one-fourth the concentration of zinc.

Example 24

This example illustrates sorption of silver (I) by sulfidized red mud (SRM). The procedure of Example 15(a) was repeated using 3.15 ppm silver (I). The results are shown in Table XII below.

TABLE XII Silver I (ppm) Control 3.15 24(a) SRM-3 filtrate N.D.

The results demonstrate that SRM-3 is an excellent sorbent for silver ion.

Example 25

This example shows sorption of gold I by sulfidized red mud (SRM). The procedure of Example 19(a) was repeated using 0.703 ppm gold III. The results are shown in Table XIII below.

TABLE XIII Gold III (ppm) Control 0.703 25(a) SRM-3 filtrate 0.227

The results demonstrate that SRM-3 is a good sorbent for gold (III) in that 68% is sorbed.

Example 26

This example illustrates sorption of cadmium II by sulfidized red mud (SRM) and by red mud (RM). The procedures of Examples 19(a) and (b) were repeated using 1.850 ppm cadmium. The results are shown in Table XIV below.

TABLE XIV Cadmium II (ppm) Control 1.850 26(a) SRM-3 filtrate 0.009 26(b) RM-1 filtrate 0.035

The results show that SRM-3 is significantly more efficient in removing cadmium II from water than is RM-1.

Example 27

This example shows sorption of lead ion ⁺2 by sulfidized red mud (SRM) and by red mud (RM). The procedures of Examples 19(a) and (b) were repeated using 2 ppm lead ion (⁺2). The results are shown in Table XV below.

TABLE XV Lead II (ppm) Control 2.0 27(a) SRM-3 filtrate 0.007 27(b) RM-1 filtrate 0.058

The results show that SRM-3 reduced lead content to about one-eighth of the content achieved by RM-1. The lead content of the SRM filtrate (7 ppb) met drinking water standards (currently 15 ppb).

Example 28

This example shows sorption of selenium by sulfidized red mud (SRM) and red mud (RM). The procedures of Examples 19(a) and (b) were repeated using 2.5 ppm selenium. The results are shown in Table XVI below.

TABLE XVI Selenium (ppm) Control 2.5 28(a) SRM-3 filtrate 0.24 28(b) RM-1 filtrate 2.10

The results show that SRM-3 reduced Se by about 90% while RM-1 only reduced Se by about 16%.

Example 29

This example illustrates sorption of uranium by sulfidized red mud (SRM-3) and red mud (RM-1). The procedures of Examples 19(a) and (b) were repeated using a Uranium Atomic Absorption Standard Solution containing 1000 micrograms of U (as uranyl nitrate—UO₂(NO₃)₂) and made up in varying concentrations (1.13, 10.1, and 38.0 ppm), and then treated with sulfidized red mud (SRM-3) and red mud (RM-1). In addition, a third test was performed on each uranium solution using a mixture of 5 g sulfidized red mud (SRM-3) and 5 g red mud (RM-1). The results are shown in Table XVII below.

TABLE XVII Uranium (ppm) Control A 1.13 29(a) SRM-3 filtrate 0.040 29(b) RM-1 filtrate 0.074 29(c) RM-1/SRM-3 0.031 Control B 10.1 29(d) SRM-3 filtrate 0.494 29(e) RM-1 filtrate 2.450 29(f) SRM-3/RM-1 filtrate 1.610 Control C 38.0 29(g) SRM-3 filtrate 3.950 29(h) RM-1 filtrate 6.900 29(i) SRM-3/RM-1 filtrate 4.660

The data in Table XVII (29(f)-(i)) confirm that sulfidized red mud is significantly more efficient for extraction of uranium than is red mud. Moreover, combinations of sulfidized red mud and red mud (1:1) are more effective than red mud alone. The combination of SRM and RM allows the complimentary extraction of elements while eliminating the leaching of other elements from RM.

Table XVIII below summarize the results of Examples 19-27. The last column indicates the amount (in wt %) of the target material that was removed by SRM.

TABLE XVIII % Control Removed Example Element (ppm) RM (ppm) SRM (ppm) by SRM 19 Chromium 2.240 0.018 0.005 99.997 III 20 Copper II 1.550 0.028 <0.004 99.997 Copper II 6.250 0.054 0.038 99.993 Copper II 30.500 0.073 0.040 99.999 21 Zinc II 1.850 0.035 0.009 99.995 Zinc II 2.380 0.103 0.022 99.990 22 Silver I 3.15  ND* ND 99.999 23 Gold I 0.703 ND 0.227 67.7 24 Cadmium II 1.850 0.035 0.009 99.995 25 Lead II 2.0 0.058 0.007 99.996 28 Selenium 2.5 2.1 0.24 99.904 29 Uranium II 1.13 0.074 0.04 99.964 Uranium II 10.1 2.45 0.494 99.951 Uranium II 38.0 6.90 3.95 99.896 *ND = not detectable

Example 30

This example compares SRM and RM for sorption of As, Co, Mn, and Sr. The procedure of Example 9 was repeated using solutions of arsenic (III), arsenic (V), cobalt II, manganese (II), and strontium (I), with results summarized in Table XIX.

TABLE XIX Control RM-1 % SRM-3 % Element (ppm) ppm Removed Ppm Removed Arsenic III 0.60 0.11 81.7 0.36 60.0 Arsenic V 1.60 0.21 87.8 1.15 72.0 Cobalt II 2.75 0.013 99.5 0.046 98.3 Manganese II 1.63 0.135 91.7 0.548 66.4 2.10 0.72 65.7 0.792 37.7 Strontium II 1.90 0.10 94.7 1.10 42.1 9.0 0.08 99.1 4.60 48.9 27.0 0.19 99.3 11.0 59.2

These experiments reveal that the efficiency of red Mud (RM-1) is significantly better than SRM-3 in the case of As (III), As (V), Mn (II), and Sr (II). However, the use of red mud as a sorbent is limited by the leaching of undesirable elements which can and have caused serious problems. Use of sulfidized red mud in combination with red mud allows utilization of the latter because sulfidized red mud sorbs undesirable leaching of extraneous metals from red mud itself.

Example 31

This example shows sorption of Hg (II) by various sulfidized red muds, as summarized in Table XX below.

TABLE XX Concentration of Hg (II) in Leachate (ppm) Concentration of Hg (II) in SRM-4 SRM-5 SRM-6 SRM-3 Original 5% % 5% % 5% % H₂S % solution (ppm) (NH₄)₂S Removed Na₂S Removed CaS_(x) Removed pressure Removed 4.5 0.001 100 0.449 90.0 0.005 99.9 0.004 99.9 19.6 0.0229 99.9 15.4 21.4 3.16 83.8 0.02 99.9

Each of SRM-3, -4, and -6 gave excellent sorption results from solutions of Hg (II) at two concentration (4.5 ppm and 19.6 ppm). It is significant that SRM-4 reduced Hg to 1 ppb, thus meeting current drinking water standards (2 ppb maximum). SRM-5 made form red mud by treatment with Na2S was much less efficient. Ammonium sulfide treatment (SRM-4) was the most effective sorbent despite the fact it had the lowest S content as shown by the analysis in Example 7.

Example 32

This example illustrates treating mercury metal with red mud and sulfidized red mud (wet). In part (a), a mixture of 10 g mercury metal, 50 g red mud, and 100 g demineralized water was rapidly mixed in a Waring Blender for 10 minutes. The aqueous slurry of red mud was separated from mercury in a separatory funnel. The slurry was filtered, dried at 80° C. for 4 hours, then ground in a coffee grinder for 3 minutes, and submitted for mercury analysis.

In part (b), the procedure of part (a) was repeated using SRM-2. In part (c), the procedure of part (a) was repeated using SRM-410, which was prepared by reaction of red mud and 10% ammonium sulfide. Results for parts (a)-(c) are shown in Table XXI below.

TABLE XXI Example Reagent % Hg sorbed 32(a) RM-1/Hg 1.27 32(b) SRM-2/Hg 0.55 32(c) SRM-410/Hg 1.65

The results show that sulfidized red mud SRM-410 of Example 32(c) was about 30% more effective than red mud (RM-1) in sorbing mercury.

Example 33

This example illustrates treating mercury metal with red mud and sulfidized red mud (dry). In part (a), a mixture of 10 g mercury metal and 50 g red mud was rapidly mixed in a Waring Blender for 10 minutes. Demineralized water (100 g) was added to the mixture and mixing in the blender resumed for 5 minutes. The aqueous slurry of red mud was separated from mercury in a separatory funnel. The slurry was filtered, dried at 80° C. for 4 hours, then ground in a coffee grinder for 3 minutes, and submitted for mercury analysis.

In part (b), the procedure of part (a) was repeated using SRM-2. In part (c), the procedure of part (a) was repeated using SRM-410, which was prepared as described in Example 32 above. The results are provided in Table XXII below.

TABLE XXII Example Reagent % Hg sorbed 33(a) RM-1/Hg 1.84 33(b) SRM-2/Hg 6.34 33(c) SRM-410/Hg 5.58

The results show that sulfidized red mud SRM-2 and SRM-410 sorbed over three times as much mercury than did red mud (RM-1). The sorption procedure in Example 33, which used direct contact of the sulfidized red mud and mercury (without water present initially), was much more effective than the procedure in Example 32, which initially added water to the mercury and sulfidized red mud.

Example 34

This example shows sorption of thorium (IV), as Th(NO₃)₄.11₂0, by RM-1 and SRM-3. In part (a), 10 g of sulfidized red mud (SRM-4) was slurried for 30 minutes with 1 kg demineralized water containing 1 ppm thorium. The slurry was filtered and analyzed for thorium.

In part (b), the procedure of part (a) was repeated using 5 ppm thorium. In part (c), the procedure of part (a) was repeated using 10 ppm thorium. In part (d), the procedure of part (a) was repeated using 20 ppm thorium. The procedures of parts (a)-(d) were then repeated using red mud. The results are summarized in Table XXIII below.

TABLE XXIII Th (ppm) in Leachate Example Control SRM-4 RM-1 34(a) 0.956 ND* 0.051 34(b) 4.930 ND 0.260 34(c) 10.500 ND 0.564 34(d) 19.400 ND 0.921 *ND = not detectable

The results show that sulfidized red mud SRM-4 was very effective (essentially quantitative) for thorium sorption.

Example 35

This example compares sedimentation rates of SRM-3 and RM-1. In the course of tests on metal sorption from aqueous solutions by sulfidized red mud and red mud, it was found that in all cases, sulfidized red mud exhibited significantly faster filtration rates than red mud. Red mud is very hydrophilic but conversion of red mud to sulfidized red mud transforms it to a lyophobic particle which is more readily dewatered. The unexpected improvement of dewatering behavior is shown in the following experiment:

A dispersion of 50 grams of RM-1 in 500 ml demineralized water was prepared by rapid mixing in a Waring Blender for 10 minutes. The experiment was repeated using 50 grams of SRM-3 in 500 ml demineralized water.

Both freshly prepared slurries were allowed to settle undisturbed at ambient temperature (25° C.) for a period of 72 hours. After 72 hours, the RM-1 dispersions had settled to give a clear supernatant layer of only 1 cm. The remaining slurry consisted of dispersed RM-1 with no visible sediment.

During the 72 hour period, the SRM-3 slurry completely settled to furnish a sedimentary layer about 1 cm deep and a clear supernatant layer 11.5 cm above the sediment.

These results clearly show the total alteration of surface chemistry and improved dewatering characteristics of red mud by relatively small degrees of sulfidation.

Example 36

Five kilograms of sulfidized red mud from Example 4 was mixed with three kilograms of water containing 50 grams of sodium silicate in a rotating spherical pelletizer (candy pan) for 30 minutes and then screened to reject and recycle plus 6 mm and minus 3 mm particles. The resulting pellets were dried for four hours at 110° C. The pellets were packed in a filter bed 60 cm deep and used to filter dilute solutions of heavy metals.

Example 37

A sample of red mud as prepared according to Example 1 is taken to constitute Sample A, a control untreated red mud that had not been sulfidized. Sample B was prepared by sulfidizing red mud (A) at 121° C. and at a pressure of 30 psi in a Parr Bomb using H₂S as the sulfidizing agent as in Example 3. Table XXIV illustrates the results of analysis by The Mineral Lab, Inc. using X-Ray Diffraction.

TABLE XXIV Approx. Wt % Mineral B (Sulfidized Name Chemical Formula A (Red Mud) Red Mud) Hematite Fe₂O₃ 37 22 Goethite FeO(OH) 10 10 Gibbsite Al(OH)₃ <10 15 Boehmite AlOOH — — Calcite CaCO₃ <10 <10 Anatase TiO₂ <3 — Perovskite CaTiO₃ — <10 Ilmenorutile (Ti,Nb,Ta,Fe)O₂ —  <5? Pseudorutile Fe₂Ti₃O₉ —  <5? Rutile TiO₂ — — Quartz SiO₂ — — — CaTi₃Al₈O₁₉ — — — Na₈Al₆Si₆O₂₄SO₄•3H₂O 17 <10 Amorphous — <20 <25 Unidentified — <5  <5

The results of the analysis shows that each of the Samples A and B contained amorphous material. Pyrrhotite was not detected in Sample B, a material that is the reaction product of the sulfidization of red mud as taught herein.

Example 38

The procedure detailed in Example 1 was repeated with substitution of red mud received from Noranda Aluminum Company of Gramercy, La. for the red mud received from Sherwin Alumina Company. The Noranda red mud was analyzed for moisture content and found to be 53.8% solids. Two slurries of the Noranda red mud having 25% solids with volumes of six (6) liters were made up, the weight of each slurry being approximately 7.54 kilograms. The slurries were respectively referred to as Sample A and Sample B. Sample A was mixed at high speed for four hours using a laboratory stirrer. The pH of Sample A was measured to be 10.34. Sample B was treated with 500 grams of 20% ammonium sulfide solution and the admixture was heated to 60° C. for one hour and allowed to cool to room temperature. The resulting slurry containing sulfidized red mud exhibited a pH of 9.48, this sulfidized slurry being referred to as sulfidized Sample B. A portion of Sample A and a portion of sulfidized Sample B were each vacuum filtered, the filtrates reslurried to 25% solids and spray dried. Particle size analysis of the resulting spray dried materials indicated no significant difference in particle sizes in the two resulting slurries.

Example 39

In preparation for testing of Sample A and Sulfidized Sample B for Example 38, 10 ml of 0.14N mercury (II) nitrate solution was added to 5 liters of distilled water. One liter of the resulting solution was reserved as a control designated hereinafter as 062711-A.

Example 40

Sample 062711-B was prepared to contain 40 grams of 25% solids sulfidized red mud slurry taken from Sulfidized Sample B from Example 38. Sample 062711-B, unfiltered and undried, was diluted to one liter of liquid using water.

Example 41

Sample 062711-C was prepared to contain 10 grams of filtered andspray dried material derived from Sulfidized Sample B from Example 38 in one liter of water.

Example 42

Sample 062711-D was prepared to contain 40 grams of 25% solids taken from Sample A from Example 38, the slurry of Sample A not having been filtered or dried, in one liter of distilled water.

Example 43

Each of the Samples prepared in Examples 39 through 42 were mixed in a Waring Blender for 5 minutes, filtered using Whatman 54 paper, and filtered once more using a Millipore filter equipped with a membrane with 2 cc of 70% nitric acid being added to each sample as a stabilizer prior to shipment for resting at Altamaha Laboratories.

Table XXV provides mercury sorption test results:

TABLE XXV Sample Mercury ppm Control 062711-A 37.00 10 ml of 0.14N Mercury (II) Nitrate solution added to 10 kilograms of distilled water 062711-B 0.000919 Sulfidized Red Mud Slurry: Not Filtered or Dried 40 grams of 25% solids sulfidized red mud slurry diluted to one liter of slurry 062711-C 0.0874 Sulfidized Red Mud Slurry: Filtered and Dried 10 grams of filtered and spray dried sulfidized red mud diluted to one liter of slurry 062711-D 2.27 Red Mud Slurry: Not Filtered or Dried 40 grams of 25% solids red mud slurry diluted to one liter of slurry

Conclusions evident from Table XXV are that sulfidized red mud that is not filtered and dried, Sample 062711-B, was approximately ten times more efficient in sorbing mercury than the same slurry that was previously filtered and dried, Sample 062711-C. Both samples 062711-B and 062711-C were significantly more efficient in sorbing mercury compared to unsulfidized red mud, Sample 062711-D.

Two slurries of ten grams each respectively of spray dried red mud and spray dried sulfidized red mud in one liter of distilled water were prepared using a Waring blender for five minutes. Each slurry was poured separately into a Buchner funnel equipped with a Whatman 54 paper and vacuum was applied. Filtration of the liquid from the slurry of red mud required 17.5 minutes while filtration of the liquid from the sulfidized red mud slurry required 5.0 minutes.

Red mud has previously been suggested as a component of a sorbing agent for wastewater treatment. Lopez et al in Wat. Res. Vol. 32, No. 4, pp. 1314-1322, 1998 combined red mud with CaSO₄ to form aggregates stable in aqueous media, these aggregates being used to sorb impurities from wastewater streams. However, Lopez et al did not address the problem of heavy metal shedding from such aggregates or from red mud itself when used as a sorbent particularly in aqueous systems.

Use of sulfidized red mud for treatment of waste effluent streams and particularly waste waters including sewage at various stages of treatment improves over the use of red mud whether or not aggregated with other substances by the fact that sulfidized red mud does not release heavy metals into the effluent streams. As noted herein, the use of sulfidized red mud in effluent treatment including wastewater treatment such as sewage treatment exhibits a number of other significant advantages and improvements over prior sorbing processes and agents.

Sulfidized red mud as disclosed herein is particularly useful in the treatment of sanitary waste water in the removal or reduction of TDS (Total Dissolved Solids) and phosphorus. Such treatment of sanitary waste water from typical oxidation ponds results in reduction of TDS and P, results consistent with the sorptive properties of sulfidized red mud for various contaminants in water. As with uses previously described and as described herein, a red mud slurry can be directly sulfidized and used as produced without filtration or drying.

Example 44

A control sample and a test sample of sanitary waste water taken from Oxidation Pond 1 at New Hope Plantation Mobile Home Park, Brunswick, Ga., were tested. The control sample was not treated and thus is labeled “Untreated” in Table XXVI. The untreated control sample was tested for TDS, P and Fecal Coliform bacteria. The test sample was shaken with 10% by weight of sulfidized red mud containing 25% solids, 5% (NH₄)₂S based on red mud for ten minutes. The results were obtained with a single treatment.

TABLE XXVI Treated with Detection Units Untreated Sulfidized Red Mud Limit TDS mg/liter 89 71 5.0 P mg/liter 1.17 0.359 0.1 Fecal mpn/100 ml ≧1600 ≧1600 2.0 Coliform

As taught in U.S. application Ser. No. 12/796,066, filed Jun. 8, 2010, by the same inventor and incorporated in its entirety hereinto by reference, high quality water suitable for distribution and consumption by humans and animals as well as for use in industrial processes is produced by the removal of discolored organic compounds through use of sulfidized red mud as an effective sorbent. Discolored organic compounds are contaminants of aqueous streams such as discharges from food processing, mining waste inter alia as well as transportation, sewage and storm runoff. Environmental regulations have been enacted to assure aesthetic appearance of public waterways by setting color standards for industrial discharges such as from paper mills and the like. Removal or reduction of concentrations of discolored organic compounds is accomplished according to present teachings in a manner similar to that disclosed herein for treatment of waste waters for removal of a variety of contaminants present in water.

Compounds considered to be undesirable discolored organic compounds include but are not limited to humic acids, fulvic acids, tannins and organic compounds formed by degradation of plant residues as well as organic compounds formed during industrial processes such as pulping and paper manufacture. These compounds and materials are very hydrophilic and not easily separated from water. Other natural and industrial contaminants found in surface and subsurface water include phthalates, bisphenol compounds, hormones, insecticides, herbicides and pharmaceutical and illicit drug residues. Removal of such compounds by readily operable and low cost processing is possible through treatment of aqueous solutions containing such compounds and materials as described herein.

Treatment of a medium containing discolored organic compounds as well as other contaminants is effected by contacting the medium with a sorbent comprising sulfidized red mud and separating the sorbent from the medium. The sorbent, containing adsorbed contaminants, can be separated from the medium using techniques including sedimentation, filtration and centrifugation. A sorbent containing or comprising sulfidized red mud can be slurried with the medium containing contaminants. The sorbent can alternatively be provided in the form of pellets or the like through which the medium is passed. Amounts of sulfidized red mud used in processing can vary over a wide range depending on factors such as the identity and relative amounts of the contaminant or contaminants present in the medium. Relatively small quantities of discolored organic compounds, for example, can be effectively sorbed with relatively small quantities of sulfidized red mud. By way of example, the amount of sulfidized red mud may range from about 0.005 to be 0.5 grams per milliliter of medium and often ranges from about 0.01 to about 0.1 gram per milliliter.

The extent to which a contaminant or contaminants may be removed from a medium will vary depending on such factors as whether the process is intended to produce potable water. The extent of removal may be quantified using any known technique. In the case of removal of discolored organic compounds, colorimetric scales are typically used, such as color value (CV) and/or absorbance. The extent of removal of contaminants may be increased, for example, by implementing multiple passes or stages as needed to achieve desired optical properties and/or purity.

Example 45

This example illustrates clarification of Okefenokee Swamp water with sulfidized red mud. 500 ml of Okefenokee Swamp water (Sample I) was adjusted to pH 7 with dilute NaOH and mixed with 10 grams of sulfidized red mud (SRM) made with 10% ammonium sulfide in a Waring blender at high speed for 5 minutes. The mixture was transferred to a beaker and allowed to stir an additional hour using a magnetic stirrer. The suspension was filtered and the color value of the filtrate was determined with a LaMotte TC-3000e colorimeter. Another 10 grams of sulfidized red mud (SRM) was then added and the procedure was repeated a second time (2^(nd) Pass). The filtrate was again evaluated for color. Results are given in Table XXVII and showed that the treated sample was nearly colorless.

TABLE XXVII Absorbance Testing of Okefenokee “Black” Water (Sample I) Sample Designation Color Value (CV) (375 mm) Control (untreated) 347 1^(st) Pass SRM 38.9 2^(nd) Pass SRM 18.8

Another sample of Okefenokee “Black” Water (Sample II) was treated with sulfidized red mud according to the above procedure. The absorbance was reduced 90% to nearly colorless, as shown in Table XXVIII.

TABLE XXVIII Absorbance Testing of Okefenokee “Black” Water (Sample II) Sample Designation Absorbance* Control (untreated) 0.063 Sample II 0.0063 *Fisher Genesys5 Spectrophotometer 500 mm

While particular embodiments of the present invention have been described and illustrated, it should be understood that the invention is not limited thereto since modifications may be made by persons skilled in the art. The present application contemplates any and all modifications that fall within the spirit and scope of the underlying invention disclosed and claimed herein. 

1. A process of dewatering red mud, comprising reacting the red mud to be dewatered with a sulfidizing compound at a reaction temperature of up to about 200° C. and a reaction pressure from atmospheric pressure up to about 30 psi to form a dispersion of sulfidized red mud in water, and allowing the dispersion to settle for a sufficient time to form a sedimentary layer and a supernatant layer.
 2. The process of claim 1 and further comprising separating the sedimentary layer comprised of sulfidized red mud from the supernatant layer.
 3. The process of claim 2 wherein the sedimentary layer is separated from the supernatant layer using at least one of filtration and centrifugation.
 4. The process of claim 1 wherein the dispersion is allowed to settle under the influence of gravity.
 5. The process of claim 1 wherein the sulfidized red mud is an amorphous material.
 6. The process of claim 5 wherein the sulfidized red mud is devoid of pyrrhotites.
 7. The process of claim 1 wherein the sulfidized red mud is formed in a system absent added hydrogen molecules.
 8. The process of claim 1 wherein the sulfidized red mud contains from about 0.2 to about 10 weight percent sulfur above residual sulfur initially present in the red mud prior to reaction with the sulfidizing compound.
 9. The process of claim 1 wherein the sulfidizing compound is selected from the group consisting of H₂S, Na₂S, K₂S, (NH₄)₂S, CaS_(x) and combinations thereof.
 10. The process of claim 1 wherein the sulfidized red mud is formed at a reaction temperature from ambient temperature up to about 60° C.
 11. The process of claim 1 wherein the sulfidized red mud is formed at ambient temperature.
 12. A method for processing a slurry of red mud and water, comprising reacting the red mud with a sulfidizing compound at a reaction temperature of up to 200° C. and a reaction pressure from atmospheric pressure up to about 30 psi to form an amorphous sulfidized red mud, filtering the sulfidized red mud to form a filter cake, and drying the filter cake at a temperature of at least 100° C. for at least 30 minutes.
 13. The method of claim 12 wherein the filter cake is dried for at least 120 minutes.
 14. The method of claim 12 wherein the sulfidized red mud is devoid of pyrrhotites.
 15. The method of claim 12 wherein the sulfidized red mud is formed in a system absent added hydrogen molecules.
 16. The method of claim 12 wherein the sulfidized red mud contains from about 0.2 to about 10 weight percent sulfur above residual sulfur initially present in the red mud prior to reaction with the sulfidizing compound.
 17. The method of claim 12 wherein the sulfidizing compound is selected from the group consisting of H₂S, Na₂S, K₂S, (NH₄)₂S, CaS_(x) and combinations thereof.
 18. A method for processing a slurry of red mud and water, comprising reacting the red mud with a sulfidizing compound at a reaction temperature of up to 200° C. and a reaction pressure from atmospheric pressure up to about 30 psi to form an amorphous sulfidized red mud, centrifuging the slurry to form a layer of sulfidized red mud and a supernatant layer, removing the supernatant layer from the layer of sulfidized red mud, and drying the layer of sulfidized red mud at a temperature at least 100° C. for at least 30 minutes.
 19. The method of claim 18 wherein the layer of sulfidized red mud is dried for up to 120 minutes.
 20. The method of claim 18 wherein the sulfidizing compound is selected from the group consisting of H₂S, Na₂S, K₂S, (NH₄)₂S, CaS_(x) and combinations thereof.
 21. The method of claim 18 wherein the sulfidized red mud contains from about 0.2 to about 10 weight percent sulfur above residual sulfur initially present in the red mud prior to reaction with the sulfidizing compound.
 22. A sorbing process for treating a fluid containing contaminants which are to be removed, comprising the steps of: contacting the fluid with sulfidized red mud to sorb the contaminants; and, separating the sulfidized red mud and sorbed contaminants from at least portions of the fluid.
 23. The process of claim 22 wherein the fluid is waste water containing phosphates, total dissolved solids including organics and bacteria.
 24. The process of claim 22 wherein the sulfidized red mud exists as an aqueous slurry.
 25. The process of claim 22 wherein the separating step comprises static sedimentation or accelerated sedimentation.
 26. In a process wherein bauxite ores are treated in the production of alumina with a red mud slurried in a highly caustic liquor being produced as a by-product, the improvement comprising the steps of: sulfidizing the red mud slurried with the caustic liquor to form a slurry of sulfidized red mud and caustic liquor; and, separating the sulfidized red mud from at least portions of the caustic liquor.
 27. In the process of claim 26 wherein the improvement further comprises the steps of recycling the at least portions of the caustic liquor to treatment of the bauxite ores.
 28. In the process of claim 26 wherein the separating step comprises static sedimentation.
 29. In the process of claim 26 wherein the separating step comprises accelerated sedimentation by centrifugal or cyclonic hydroclassification.
 30. In the process of claim 26 wherein the improvement further comprises placing the sulfidized red mud and at least portions of the caustic liquor in a settling pond. 